A fluid end is a high-pressure, reciprocating pump which contains a bore where the plunger reciprocates. Fluid ends could have several plungers and its corresponding plunger bores. It is public knowledge in the pressure pumping industry that packing bore washout is one of the leading causes of fluid end failure. In addition, typical steel uses about 32 Rockwell C hardness where washout and cavitation are a problem. Further, typical steel processing has to be forced casting at about 14,000-15,000 psi. The steel is machined to particular client specifications.
Paragraphs below are described in an article written by Mark Nowell, believed to be the owner of a pump/valve source. It was published in Upstream Pumping Magazine in October 2016, which outline problems and failures in fluid ends. The author defines “Packing Bore Washouts” as the number 2 cause of Fluid Ends' Failure. See Nowell, Mark. “The 5 Failures of Fluid Ends.” Upstream Pumping, October, 2016. Accessed Nov. 15, 2016, http://www.upstreampumping.com/article/well-completion-stimulation/2016/5-failures-fluid-ends, all of which is incorporated herein by reference thereto.
The article sets out common problems to avoid for longer equipment life. “The fluid end is a critical component of the pressure pumping industry. Fluid ends also can be the biggest heartburn for frac companies when they fail prematurely. Extreme environments such as 100 mesh frac sands, ever-increasing pressures, recycled water, advanced chemicals and slickwater all contribute to fluid end failure in as little as 100 to 500 pumping hours. In today's market, that is an expensive problem. This article looks at five consistent failure points of the frac fluid end. Solving these problems can extend the life of the fluid end and reduce the cost per hour. Given the industry's current climate, saving money and increasing profitability and productivity are a big win.” Id.
Another failure is described as packing bore washouts. “Properly maintaining fluid ends in high-cycle environments is not easy, since packing bores can wash out at any time. If a packing or grease system fails, the packing bore gets cut by the high-pressure water, causing it to lose its ability to seal. The use of stainless steel fluid ends achieves higher cycle hours, but with those longer hours of operation, the packing begins to wear into the packing bore, creating waves. This is called washboarding.
Eventually, the packing bore becomes so severely washboarded that the packing will not seal. Washouts and washboarding can be weld repaired, but that drastically reduces the strength of the fluid end because welded material cannot compare to the strength of forged stainless steel. Weld repairs lower the endurance limit of the fluid end at the surface.
Cracks in stainless fluid ends are found more frequently in welded areas than in non-welded areas.” Id.
A known stuffing box sleeve does not house the seal on the outside diameter, transferring seal wear from the body to the replaceable sleeve.
“The best solution for packing bore problems was invented many years ago when reciprocating pump companies began using removable stuffing boxes or stuffing box sleeves in their pumps. Stuffing boxes house the packing that goes into the fluid end, becoming a sacrificial piece.
Washouts still occur when using stuffing boxes, but instead of weakening the fluid end by weld repairs, transferring the wear to the replaceable stuffing box is a better solution.
Stuffing boxes and sleeves are a move in the right direction, but the issue of a solid seal remains. Because the outside diameter of the boxes and sleeves must seal on the inside diameter of the fluid end, the sealing area becomes washboarded and wears out the fluid end, just like the packing in the bore.” Id.
An attempt to solve these sealing problems is known. “Instead of using off-the-shelf seals that may not provide the best seal, they use engineered seals that fit perfectly into a groove machined into the fluid end. This new solution provides a more consistent and reliable seal while transferring the wear from the inside diameter of the fluid end to the outside diameter of the stuffing box sleeve. Now the stuffing box sleeve is a sacrificial piece in two places: on the inside diameter where the packing seals and the outside diameter against the fluid end.” Id. The sleeved stuffing box, indicated generally at 150, fights washouts by becoming a sacrificial piece (see FIG. 5 of the present application).
The instant Applicant submits that there have been numerous attempts in the industry to overcome the wear issues with fluid ends. Some of these attempts will now be explained, as follows:
Weld repair: This solution is the most widely used, and consists of machining the washed-out packing bore oversized, adding a layer of welded material, and then re-machining the packing bore to its specification size. The welded material is softer than the originally forged parent metal, and eventually fails faster during pumping.
Replaceable the stuffing box (described in the article set forth previously): This solution adds complexity to the fluid ends in both, their initial assembly and their maintenance on-the-field, because it increases the number of components it requires a separate stuffing box and additional seals. It also adds complexity to the machining of the fluid ends blocks, which require a complete redesign on the packing bore area. Moreover, since the stuffing boxes are replaceable pieces, because they are still affected by washout, the cost of the fluid end increases over its lifetime.
An abrasive resistant insert (constructed of a ceramic, zirconium, or a composite material) indicated generally at 200: This expensive solution is cumbersome and complex to manufacture. It is also complex for the mechanical features to keep the insert in place, adding several components and more machining to the fluid end (see FIG. 6 of the present application). FIG. 6 in the present application corresponds to FIG. 5 of U.S. Patent Publication No. US 2013/0319220 A1, to Luharuka et al, publication date Dec. 5, 2013, all of which is incorporated herein by reference thereto.
The problem with the above mentioned solutions is that the sealing areas are prone to washboarding and the washout problem still remains unsolved.
Accordingly, there remains a need for an effective hardened insert or liner for fluid ends with a predetermined hardness for increased durability and minimizing washout problems.